1. Field of the Invention
This invention relates to sputtering equipment for deposition of materials and, more particularly, to improved refractory metal targets for such equipment.
2. Prior Art
Sputtering is a physical process used for the deposition of thin films. Sputtering uses the kinetic energy of accelerated ions of an inert gas, such as argon, to transfer energy to the materials of a target. Upon impact by the accelerated ions, target material is dislodged from the surface of a target. The dislodged material is then deposited on a desired substrate. Sputtering processes are used to deposit thin films of a variety of sputtered materials on a variety of surfaces. Sputtering is often used where thin-film chemical-vapor deposition (CVD) cannot be used, such as, for example, for depositing metal alloys.
Planar sputter targets are used in several of the more advanced machines for physical vapor deposition, such as the Anelva 1015, the Applied Materials Endura 5500, and the Materials Research Corporation 662. The magnetron cathode in these machines generates a broad band of erosion in the target. This produces a very uniform film of deposited metal and fairly uniform step coverage at surface discontinuities.
However, the symmetric magnetic field generated by some of the cathodes results in a single erosion groove in the sputter target, leaving other areas of the target which are not eroded. During the sputtering process, some metal is scattered back toward the target and is deposited onto the non-eroded areas of the target, producing multiple layers of re-deposited material. For refractory metals, temperature cycling of these multiple layers of re-deposited material causes delamination or peeling of these re-deposited layers from the target. This delamination or peeling phenomena produces flakes of material which produces defects in the sputtered thin-films deposited, for example, in the fabrication of semiconductor integrated-circuits, resulting in greatly decreased product yield.
One technique to attempt to avoid this problem is to modify the cathode design so that the magnetic field sweeps the plasma across the entire target surface to provide erosion of the entire surface of the target area. Because there are no areas of the target where a film can build up by re-deposition of the sputtered material, there is no occurrence of delamination or peeling of re-deposited material from the target.
Another technique to avoid delamination is to roughen the surface of the center of the target to increase adhesion of the re-deposited film. However, the roughened area of the target can become a constant source of film defects if the size of the roughened area does not exactly match the size of the non-eroded area of the target.
Consequently, the need has arisen for a technique to reduce the yield of integrated-circuit product by eliminating the peeling and flaking of re-deposited materials from the non-eroded areas of refractory metal sputter targets, while not contaminating the film being deposited. It is desirable that the technique work with existing cathode designs and be cost effective.